Long-persistent luminescent (LPL) materials store photon energy as charges and emit light over extended periods via charge recombination. LPL decay typically follows a power law rather than an exponen Show more
Long-persistent luminescent (LPL) materials store photon energy as charges and emit light over extended periods via charge recombination. LPL decay typically follows a power law rather than an exponential decay, enabling confirmation of charge accumulation from emission decay characteristics. While charge generation in organic materials has been widely studied at donor-acceptor (D/A) interfaces, it remains underexplored in single-component luminescent materials. Here, we investigate charge generation in organic solids by dispersing a luminescent molecule in various hosts and performing slow transient emission analyses. This approach enables the evaluation of ionization through accumulated triplet excited states and the detection of weak charge accumulation, which are difficult to capture using conventional transient techniques. Our results show that ionization in single-component materials proceeds through resonance-enhanced multiphoton ionization, although it is less efficient than at D/A interfaces. This approach provides insight into long-term photophysical and photochemical processes such as photodegradation. Show less
Long-persistent luminescence (LPL) materials have applications from safety signage to bioimaging; however, existing organic LPL (OLPL) systems do not align with human scotopic vision, which is sensiti Show more
Long-persistent luminescence (LPL) materials have applications from safety signage to bioimaging; however, existing organic LPL (OLPL) systems do not align with human scotopic vision, which is sensitive to blue light. We present a strategy to blueshift the emissions in binary OLPL systems by upconverting the charge-transfer (CT) to a locally excited (LE) singlet state. Through rigorous steady-state and time-resolved photoluminescence spectroscopy and wavelength-resolved thermoluminescence measurements, we provide the direct experimental evidence for this upconversion in OLPL systems featuring small energy offsets between the lowest-energy CT and LE singlet states. These systems exhibited strong room temperature LPL, particularly when extrinsic electron traps are added. Importantly, the developed OLPL system achieved Class A (ISO 17398) LPL, matching well with human scotopic vision. The findings not only elucidate the role of small energy offsets in modulating LPL but also provide potential avenues for enhancing the efficiency and applicability of OLPL materials. Show less